Abstract: Environmental toxins have been shown to induce genotoxic and genome-destabilizing DMA lesions that must be repaired to prevent oncogenesis. Recently, concerns have arisen regarding the relative safety of organophosphate pesticides to the environment. Organophosphate residues are found in human blood and urine samples, livestock, avian species, soil samples, drinking water and foods for human consumption. Chronic exposure to pesticides, including organophosphates, leads to an increased incidence of DMA damage and chromosomal alterations, suggesting that pesticides may act as environmental carcinogens. This pilot project will therefore study genomic instability induced by the organophosphate Isofenphos (IFP). Chronic IFP poisoning has been linked to myeloid metaplasia and acute myelogenous leukemia. Such oncogenic properties likely stem from IFP induced chromosomal aberrations observed in human lymphocytes. Here we propose to extend these observations by determining putative mechanism(s) utilized by IFP to induce chromosomal damage and create genomic instability in lymphocytes. In addition, we will identify DMA repair enzymes likely to be involved in reversing IFP-induced DNA damage. Relevance: This pilot project will converge the toxicology expertise of Dr. Heyliger and the DNA damage and repair expertise of Dr. Sobol to dissect mechanisms associated with toxicity and carcinogenicity associated with environmental toxicants such as isophenfos